1. Field of the Invention
The invention relates to improvements in a copying apparatus having adaptor type paper feeding units which augment the paper feeding capability of the copying apparatus, if occasion demands.
2. Description of the Prior Art
In recent year, there have been proposed adaptor type paper feeding units capable of augmenting copying capability in the case of a large amount of copies or the like. In the drawings, namely, FIG. 1 illustrates a copying apparatus having such a detachable paper feeding unit A as has been proposed. In this type of copying apparatus, other additional paper feeding units A may be attached, if required, to the lower part of copying apparatus B being thereto provided with two sets of paper feed tables 2A, 2B each capable of loading paper feed cassettes 1A, 1B, respectively. More detailedly, in this type of copying apparatus, recording paper inlet 5 is provided at the bottom of copying apparatus B so that recording papers X may be fed in from paper feeding unit A at the midpoint of paper feeding passages 4 from the aforementioned paper feed tables 2A, 2B respectively to photoreceptor drum 3. Accordingly, recording paper X having been stored in recording paper cassette 1C is fed in as occasion demands to paper feeding passage 4 of copying apparatus B by the action of paper drawing-out roller 6 located above paper feed table 2C for paper feeding unit A.
In such a copying apparatus constituted as mentioned above, however, there is a problem that the distance along the paper feeding passage from paper feed table 2C extended over to photoreceptor drum 3, that is, namely, paper feed path L.sub.2 in paper feeding unit A, becomes much longer than the distances along the paper feeding passage from paper feed table 2A, 2B respectively to photoreceptor drum 3, that is, namely, paper feed path L.sub.1. Resultantly, in the conventional types of copying apparatuses, there is a problem of paper feeding speeds when using paper feeding unit A, that is, that recording paper may not be fed unless the timing of paper feeding is slower than that of paper feeding by means of paper feed table 2C. Therefore, the lowering of the copying speeds of copying apparatuses have been unavoidable when paper feeding unit A has been used therewith.
FIG. 5 is a time-chart showing the abovementioned relation to be originated when a continuous copying is operated. FIG. 5(1) is a time-chart for a copying apparatus being provided with paper feeding tables 2A, 2B only, and which shows the operation of primary paper feeding roller R.sub.1 provided on paper feeding tables 2A, 2B; the operation of secondary paper feeding roller R.sub.2, that is also called a registration roller, for feeding paper-sheets synchronously with the revolution of an electrophotosensitive receptor drum; and the operation of recording paper detecting sensor S.sub.0 provided immediately before the secondary paper feeding roller R.sub.2 ; with demand signal OD generated from the copying apparatus to revolve the secondary paper feeding roller R.sub.2.
FIG. 5(2) is a time-chart for the conventional type of copying apparatus having an added paper feeding table 2C, and this time chart shows the operation of paper drawing out roller 6 located on the upper part of paper feeding table 2C; the operation of the aforementioned secondary paper feeding roller R.sub.2 ; and the operation of the aforementioned recording paper detecting sensor S.sub.0 ; with the aforementioned demand signal OD. In comparison with the case of FIG. 5(1), the number of copied papers per unit of time will decrease in this case.